1. Field of the Invention
This invention relates to plasticized compositions of polyphosphazene homopolymers and copolymers, to flexible and semi-rigid films and foams produced from said plasticized compositions, and to a process for preparing said plasticized compositions, films and foams. The plasticized compositions of this invention exhibit excellent flame-retardant and film-forming properties. Films and foams prepared from the plasticized polyphosphazenes exhibit excellent flame-retardant properties and produce low smoke levels or essentially no smoke when heated in a flaming or nonflaming mode.
2. Description of the Prior Art
The preparation of polyphosphazene polymers has been disclosed in U.S. Pat. No. 3,370,020, Allcock; 3,856,712, Reynard et al; 3,856,713, Rose et al; and 3,883,451, Reynard et al. Recently, the blending of phosphazene-epoxy prepolymers with organic liquid prepolymers, such as phenolics, epoxides, polyurethanes and polyesters, and subsequently curing such blends, has been disclosed in U.S. Pat. No. 3,867,334, Frank et al. Poly(fluoroalkoxyphosphazene) vulcanizates have similarly been blended or plasticized with low molecular weight fluoroalkoxide oils, as disclosed in U.S. Pat. No. 3,943,088, Kyker et al. However, the products produced by the methods of the prior art have widely varying processing and physical characteristics which, in many cases, limit their utility, particularly when it is desired to prepare films or foams.
In our U.S. Pat. application Ser. No. 705,116, filed July 12, 1976, improved phosphazene polymers have been disclosed comprising a blend of a polyphosphazene having a Young's modulus of up to about 5 .times. 10.sup.8 dynes/cm.sup.2 and at least one polyphosphazene having a Young's modulus of at least 5 .times. 10.sup.8 dynes/cm.sup.2. These blends form excellent sheets, films and foams.